Electrical duplexer employing a traveling wave tube as a directional coupler



March 1962 J L. CARTER ETAL 3,02

ELECTRICAL CUPLEXER EMPLOYING A TRAVELING WAVE TUBE AS A DIRECTIONAL COUPLER Filed Dec. 6, 1960 ISOLATION ELECTRoN GUN LD TwT-L i I HELIx 3 HELIX COLLECTOR I I I 2% I 7 I2 H COMMON LOW TRANS. BIREC. REE RECEIVER ANTENNA LOAD TRANSMITTER MATCHED 9 LOAD FERRITE cIRcuLAToR FIG. 2

ISOLATION ELECTRON GUN SH'ELD i l HELIX HELIX IcoLLEcToR I I 3 I I I 2 I 5 nuunu uuuuu 3 I k I I I ELECTRON BIAS I I4 To TuRN THE IT Low ELECTRON BEAM REF ON OR OFF. LON) FERRITE CIRCULATORS INVENTORS,

JOHN L. CARTER 8 IRVING RE/NGOLD.

ATTORNEY States 3,027,453 Patented Mar. 27, 1952 ELECTRICAL DUPLEXER EMPLOYIN G A TRAVEL- ING WAVE TUBE AS A DIRECTIGNAL COUPLER John L. Carter, Asbury Park, and Irving Reingold, Deal Park, N.J., assignors to the United States of America as represented by the Secretary of the Army Filed Dec. 6, 1%9, Ser. No. 74,208 8 Claims. (Cl. 250-13) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

The invention relates to electrical switching devices and particularly to electrical switching devices for dopicxing or other control purposes in high frequency communication systems.

A general object of the invention is to produce directional control of high frequency electromagnetic signal wave energy in such systems efiiciently and economically with equipment that requires no relatively movable parts for performing the necessary control actions.

A more specific object is to produce the signal control actions in circuits connecting a common transmitting and receiving antenna to the signal transmitter and receiver of a microwave radar or other two-way high frequency radio system such as to enable system operation alternately for signal transmission and reception with minimum adverse eiiects on the quality of signal transmission while effectively preventing undue damage to sensitive detector elements in the receiver by outgoing signal wave energy of relatively high power.

Another specific object is to provide electrical coupling between certain branches of a switching network and a high degree of electrical isolation between other branches thereof which are dependent on the direction of applied electromagnetic wave energy or the presence or absence of a controlling electron beam.

Multibranch coupling networks known as circulators utilizing the non-linear attenuation characteristics and the nonreciprocal transmission properties of ferromagnetic or other gyromagnetic materials, such as ferrite, have been previously used for such functions as duplexing and switching of electromagnetic Wave energy in microwave communication systems because their use enables the simplification of design and construction of such systerns. Such circulators have the electrical property that energy is transmitted sequentially from one port to another of an N port device (N 2) for which the attenuation between adjacent ports for energy flow in the sequence ports I to 2 to N to 1 is lower than for energy flow in the reverse sequence.

In accordance with the invention, one or more circulators are combined with the conventional traveling wave tube of the split helix type with an associated gun for applying thereto an electron beam to produce a high repetition, broadband duplexer and a high-speed, multiport switching network, respectively, having exceptionally good operation characteristics under all conditions of use including good electrical connection between certain of its branches or terminals and a high degree of electrical isolation between others of them, dependent on the direction of the electromagnetic wave energy applied to the duplexer or network or the presence or absence of a controlling electron beam.

The various objects and features of the invention will be better understood from the following detailed description thereof when it is read in conjunction with the figures of the accompanying drawing, in which:

FIG. 1 shows schematically a high repetition rate, broadband duplexer embodying the invention, applied to a microwave radar or other high frequency radio system; and

FIG. 2 shows schematically a high-speed, multiport switching network embodying the invention.

Referring to FIG. 1, the duplexer comprises a conventional traveling wave tube of the split helix type shown diagrammatically as comprising a traveling wave tube (TWT) including in different sections of the interior thereof an input helix portion 1 and an output helix portion 2 separated by an isolation shield 3, an associated electron gun 4 for impressing an electron beam on the helix portions and a circulator CNl utilizing magnetized ferrite or other gyromagnetic material. The electron gun 4 may comprise the usual cathode 5 for emitting the electrons thermionically followed by a modulating grid 6 for controlling the number of electrons that flow in the beam, the usual electron-optical focusing means and the collector anodes 7 at the end of the tube for receiving the beam.

The multibranch circulator CNl containing ferrite or other ferromagnetic elements biased transversely by a magnetic field may be of the waveguide type disclosed in the US. Patent No. 2,849,683, issued August 26, 1958, to S. E. Miller, for example, the three-branch, non-reciprocal waveguide network shown in FIG. 7 and illustrated schematically in FIG. 9 of that patent and in FIG. 1 of this application by a ring CNI with the three branches :2, b, and c which are such that all energy applied to terminal a will be coupled to terminal b with substantially no loss while a substantially high degree of isolation exists between terminals a and c. As shown in FIG. 1 of this application, the branch a of the network CNI is directly connected to the output of the signal transmitter 8 of the microwave radar or radio system so as to be supplied with the relatively high power outgoing signals at a given repetition rate during signal transmitting intervals. The branch c of CNl is connected directly to a matched resistive load 9. The branch L of CNl is connected directly to one end of the helix portion 1 of TWT and the other end of that portion is connected directly to the common transmitting and receiving antenna 10. The receiver 11 is connected to one end of the helix portion 2 and a low reflection load 12 is directly connected to the other end of that portion.

The electron beam generated by the electron gun 5 is continuously supplied to the collector 7. This beam is focused to pass through both the input helix 1 and the output helix 2. The accelerating voltage between the anode gun 5 and the collector 7 is adjusted so that the velocity of the electrons in the beam and the velocity of the electromagnetic Wave on the helix are equal when the wave propagates from the antenna 1t)- toward the circulator CNl. This direction of propagation will be referred to as the forward direction, and the direction of propagation in the path from the circulator to the antenna will be referred to as the backward direction. When the velocity of the electrons in the beam and the velocity of the forward electromagnetic wave on the input helix 1 are properly adjusted, there is an interaction of coupling between the wave on the helix and the electron beam. When the electromagnetic wave is in the backward direction there is a large difference between the beam velocity and the backward wave velocity and no interaction or coupling can occur. The amount of power that can be coupled to the electron beam is a function of the beam and helix geometry and the DC. power in the electron beam. In this case, these parameters are adjusted so that the maximum amount of RF power that can be coupled to the beam is 10 milliwatts peak; if this value is exceeded, the beam is defooused and no coupling can exist. The velocity of the forward electro' magnetic wave in the output helix 2 and the electron 3 velocity in the beam are adjusted so that there is coupling between the beam and the output helix 2; the interaction between the beam and the coupler is such that the coupling ratio is slightly greater than unity coupling.

The duplexer of FIG. 1 operates as follows: The electromagnetic pulse from the transmitter 8 is incident at port a of the circulator CNl and is transmitted with little or no loss to port b of the circulator CNl. The pulse then goes to the input helix -1 and travels in the backward direction along that helix to the antenna 10.

ince the electromagnetic wave is in the backward direction, it does not couple to the beam. Therefore, there is isolation between the transmitter 8 and receiver 11 which is connected to the output of helix 2. In any practical application, the antenna 10 will not be perfectly matched; hence, there will be some energy reflected from the an tenna. This wave will travel in the forward direction along the helix and will couple to the beam and in turn couple from the beam to the output helix 2 and finally to the receiver 11. The amount of power coupled to the receiver 11 in this fashion cannot exceed 10 milliwatts, since this is the maximum power that can be transmitted by the electron beam. During the receiving cycle of the radar system, the returning pulse which contains less than 10 milliwatts peak power enters the antenna, goes to the input helix 1 and is coupled to the beam, and is transmitted to the output helix 2 Where it is amplified to compensate for losses; and is then transmitted to the receiver 11. It should be noted that the maximum power transmitted to the receiver is limited to 10 milliwatts.

The high speed multiport switching network of FIG.

2 in accordance with the invention includes a traveling wave tube of the split helix type with an associated electromagnetic gun structure substantially identical with that used in the duplexer of FIG. 1 as indicated by the use of the same reference characters for identifying corresponding elements, and two circulators CNZ and CN3 utilizing magnetized gyromagnetic material.

The circulators CNZ and CN3 are four-port junction circulators, similar to the one described by Yoshida in.

a of the circulator CNZ is connected through the helix portion 1 of the traveling wave tube TWT directly to the input terminal or port IT of the network. The matched resistive network 13 is connected directly to the branch of the circulator CNZ opposite branch a. The two intermediate branches b and d of circulator CN2 respectively operate as two output ports of the network. The branch (1 of CNS is directly connected in series through the output terminal OT and the helix portion 2 of TWT to the low reflection load 14. The opposite branch 0 of the CNS is connected to a matched resistive load 15, and the intermediate branches b and d of that circular form two other output ports for the network.

With the electron gun biased by a voltage applied to the modulating grid 6 so that the electron beam is on, an input signal applied to the input port IT will be coupled through the input and output helix portions 1 and 2 with low loss to the output terminal OT and will be applied to branch a of CN3, and an output signal will appear at one of the output ports formed by the branch b or d of that circulator depending upon which way the circulator is switched. With the beam off, a high degree of electrical isolation exists between the helix portions 1 and 2 of TWT so'that an input signal applied to the input port IT will pass through the helix portion 1 only to the branch 0 of the circulator CNZ, and an output signal Will appear at one of the output ports formed by the branch b or d of that circulator depending upon which way the circulator is switched.

Beam switching times can be in the order of rnillimicroseconds and at high repetition rates. Other tube characteristics such as bandwidths, power limits, and limiting action are unaffected by the operation of the multiport switching network, as described above.

A wider bandwidth may be achieved by using the antireciprocal rotation of the polarization of electromagnetic wave energy produced by a magnetized element of ferromagnetic material to provide an isolator which may electrically isolate one electrical circuit from another in place of each of the circulators shown in FIG. 2. Such an isolator system is disclosed in U.S. Patent No. 2,748,353, issued May 29, 1956, to C. L. Hogan, and in his publication, The Microwave Gyrator in the Bell System Technical Journal, January 1952. However, the use of isolators in place of the circulators will reduce the output ports of the network to two.

Various other modifications of the duplexer and switching network arrangements described which are within the spirit and scope of the invention will occur to persons skilled in the art.

What is claimed is:

1. In combination in a switching network, a first terminal, a second terminal, a traveling wave tube of the split helix type having input and output helix portions in different sections thereof and an associated electron gun for generating and transmitting an electron beam through the different sections of said tube, a multibranch circulator utilizing magnetized gyrornagnetic material having the electrical property that electromagnetic signal wave energy applied to one of its branches will be electrically coupled only to a second branch for a given direction of wave transmission and to still another branch for the opposite direction of wave transmission, one branch of said circulator being connected in series with said input helix portion of said tube to said input terminal, a matched resistive load connected to a second branch of said circulator and at least a third branch of said circulator, a non-reflection load connected in series with said output helix portion of said tube to said output terminal, said input and output helix portions being electrically coupled by said electron beam to provide transmission of signal wave energy with low loss through said tube between said first and second terminals for a given operating condition of said electron gun and a given direction of transmission of the signal waves through said circulator, and to provide a high degree of electrical isolation between said first terminal and said second terminal, and to allow signal transmission with little loss between said one terminal and said third branch of said circulator through that circulator and only the input helix portion of said tube for a different operating condition of said electric gun and the opposite direction of signal transmission.

2. The combination of claim 1, in which said electron gun is conditioned at all times to transmit a generated electron beam through said sections of said tube, and the direction of signal transmission is such as to channel input signals applied to said third branch of said circulator through said one branch thereof along said input helix only to said one terminal and to substantially prevent transmission of any appreciable portion of said input signals through said input and output helix portions to said output terminal due to a high degree of electrical isolation existing between said helix portions for that direction of said input signals, and for the opposite direction of signal transmission substantially all of the input signal energy applied to said one terminal is coupled by said electron beam with little loss through said input and output helix portions of said tube to said output terminal.

3. The combination of claim 1, in which said electron gun is conditioned to transmit a signal beam to said tube sections only in alternate time intervals, and when the beam is on, the input signals applied to said one terminal are coupled by said beam through coupled input and output helix section to said second terminal with low loss and substantially none of that energy is transmitted through the circulator to said third branch thereof, and when the beam is off, the signal waves applied to said third branch of said circulator are channeled directly through the input helix portion of said tube to the input terminal, and substantially none of that energy is transmitted to said output terminal due to the high isolation existing between said input and said output helix portions for this direction of signal transmission.

4. A multiport switching network comprising a traveling wave tube of the split helix type having an input helix portion and an output helix portion in different sections of the tube and an associated electron gun for supplying thereto an electron beam, and a multibranch circulator utilizing magnetized gyromagnetic material having the electrical property that electromagnetic Wave energy applied to one of its branches will be transmitted in circular fashion around the circulator and will be electrically coupled to only one of the other branches for a given direction of wave transmission, one terminal of said network connected in series with the input helix portion to one branch of said circulator, a non-reflection load, a second terminal of said network connected in series with said second helix portion to said non-reflection load, the incoming electric wave signals applied to said one terminal in one direction being coupled by said beam through said input and output helix portions with low loss to said second terminal, substantially all of the signal wave energy applied in the opposite direction to a second branch of said circulator being channeled through said one branch thereof in series through the input helix portion to said one terminal and in substantially none of this energy being transmitted to said second terminal due to the high degree of electric isolation between the input and output helix portions for that direction of transmission.

5. In combination with a radio communication system including a common transmitting and receiving antenna and a radio transmitter and receiver respectively operative in alternate time intervals to transmit high power out; going electromagnetic signals and to detect incoming electromagnetic signals of the same frequencies, duplexing means for conditioning said system alternately for signal transmission and reception comprising a multibranch circulator using magnetized gyromagnetic material having the electrical property that elecrtomagnetic wave energy applied to one of its branches is effectively electrically coupled only to one other of the branches for a given direction of transmission and to still another of the branches for the opposite direction of transmission and a traveling wave tube of the split helix type having input and output helix portions in different sections of the tube and an associated electron gun for supplying an electron beam to said tube sections, said input helix portion being connected in series between said antenna and one branch of said circulator, a second branch of said circulator being connected to the output of said transmitter so as to receive high power outgoing signal wave energy therefrom in signal transmitting intervals, a matched resistive load connected to a second branch of said circulator, a low reflection load connected in series with the output helix portion of said tube to said receiver, most of the high power outgoing signal energy received from said transmitter in signal transmitting intervals passing through said second and said one branch of said circulator and being channeled directly through said input helix portion of said tube to said antenna for radiation thereby, the high degree of isolation between the input and output helix portions preventing any appreciable amount of this energy from reaching the receiver during signal transmitting intervals, the direction of received signal energy impressed from the antenna on said input helix portion during signal receiving intervals being such that it is effectively coupled by said electron beam through said input and output helix portions with little loss to said receiver.

6. The duplexing equipment of claim 5 in which any antenna reflection or other reflections of an undesired nature are absorbed by the matched resistive load connected to said second branch of said circulator.

7. The multiport switching network comprising a traveling wave tube of the split helix type including input and output helix portions with an associated electron gun for supplying an electron beam to said helix portions, two multibranc-h circulators utilizing magnetized gyromagnetic material having the electrical property that the electromagnetic wave energy impressed on one of its branches is transmitted in circular fashion around the branches and is coupled to only one adjacent branch for one direction of transmission and to still another branch thereof for the opposite direction of transmission, an input port of said network connected in series through the input helix portion of said tube to one branch of one of said circulators, a matched resistive load connected to a second branch opposite to said one branch of said circulator and a third and fourth branch respectively forming a first and a second output port of said network, a low reflection load connected in series through the output helix of said tube to one branch of said second circulator, a matched resistive load connected to a second branch opposite said one branch of said second circulator and an intermediate third and fourth branch of said second circulator respectively operating as a third and fourth output port of said network, means for conditioning said electron gun so that the electron beam is turned on and off during alternate time intervals, said input and output helix portions with the beam on being efiectively coupled by said beam in energy transmitting relation so that said input signals applied to said input port will be transmitted through said input and output helix portions to said one branch of said second circulator with little loss and an output signal will appear at said third or fourth output port of said network depending on which way said second circulator is switched, and with the electric beam off, a high degree of electric isolation exists between the input and output helix portions of the tube and the input signal applied to said input port of said network will be transmitted in series through the input helix portion of said tube only to said one branch of said one circulator and substantially all of this energy will appear at either the first or second output port of said network depending on which way said one circulator is switched.

8. The multiport switching network of claim 7, in which the energy appearing at said third or fourth output port of said second circulator or at said first or second output port of said network depends on the direction of the applied transverse magnetic field applied to said one and said second circulator.

No references cited. 

